A bioabsorbable coating for a surgical article comprises a copolymer manufactured from the monomer caprolactone and at least one other copolymerizable monomer. The surgical article can be a bioabsorbable suture or a ligature. The surgical suture or ligature coated with the bioabsorbable copolymer has improved knot repositioning properties.
The bioabsorbable coating of this invention has advantages over prior art coatings used with surgical sutures or ligatures. Specifically, sutures coated with the copolymer coating of this invention are less stiff than sutures using the coating described in the prior art; see examples 6 and 10 in U.S. Pat. Nos. 3,867,190 and 3,736,646 which are incorporated herein by reference. Also, the processes for coating a bioabsorbable surgical article are not clearly described in the prior art. That is, the process of this invention uses a copolymer manufactured from at least about 50 percent by weight of the monomer caprolactone and the remainder glycolide. Copolymers of these proportions are soluble in acetone, as contrasted with, for example, the copolymers of lactide and glycolide discussed in U.S. Pat. No. 4,201,216, which is incorporated herein by reference.
The use of a copolymer of caprolactone and glycolide as a suture is known in the prior art, for example, as disclosed in U.S. Pat. Nos. 4,700,704 (e.g. claim 1) and 4,605,730 (examples I to XI), and in example 5 of U.S. Pat. Nos. 4,300,565 and 4,243,775. All of these patents are incorporated herein by reference.
The use of a copolymer of at least 90% by weight caprolactone and another biodegradable monomer, e.g. glycolide, as a coating is disclosed in U.S. Pat. No. 4,624,256. See also U.S. Pat. Nos. 4,190,720 (column 1) and 3,942,532 (example II), which are disclosed in the U.S. Pat. No. 4,624,256. These two latter patent disclose a copolymer U.S. Pat. No. 4,190,720 or homopolymer U.S. Pat. No. 3,942,532 of e-caprolactone. In the U.S. Pat. No. 4,190,720, the copolymer is disclosed as a film; in the U.S. Pat. No. 3,942,532 the homopolymer is disclosed as a suture coating. It is not seen in either of the latter two patents where the respective polymers are disclosed as bioabsorbable. All of these patents are incorporated herein by reference.
The bioabsorbable coating of this invention has superior and unexpected results over the known commercially available surgical suture or ligature coatings. For example, the coating of this invention does not present a hazy appearance on a suture. The coating can be dissolved in acetone which seems to be less deleterious than other known solvents, for example, methylene chloride. Further, suture characteristics such as knot-snug-in or repositioning, knot security, and tissue drag appear to be equal to, if not better than suture coatings disclosed in the prior art.
The copolymers described in this invention are random. The term random copolymer means the result of a copolymerization reaction in which all of the monomers are charged into the reactor simultaneously. It is to be understood that variations in reaction conditions can lead to some differences in the actual degree of randomness with respect to the distribution of comonomer units in a copolymer chain.
A bioabsorbable coating for a surgical article has been invented. The coating comprises a random copolymer, from about 50 to 85 percent by weight of the copolymer consisting of linkages of formula (I): ##STR1## and the remaining linkages comprising at least one of the formulas (II) to (VIII): ##STR2##
In one embodiment, the remaining linkages are selected from the group consisting of formulas (II) and (III). In another embodiment the remaining linkages are selected from the group consisting of formula (II).
In a specific embodiment, the formula (II) is: ##STR3## In another specific embodiment, the formula (II) is: ##STR4##
In still another embodiment, formula (I) is from about 65 to 85 percent by weight. In a further embodiment, the inherent viscosity of the copolymer is about 0.2 to 1.4 dl/g (0.5 g/dl in CHCl.sub.3, 30.degree. C.) and the melting point is less than about 50.degree. C.
It is to be understood that the term strand as used in this invention can be either a multifilament or a monofilament. A multifilament is preferred. The multifilament strand can be a braid.
The surgical article coated with the above described polymers can be bioabsorbable. In one embodiment, the bioabsorbable surgical article is a suture or ligature. In a specific embodiment, the suture or ligature is manufactured from a polymer prepared from one or more monomers selected from the group consisting of lactides, carbonates and lactones. If the polymer in a strand, for example a suture or ligature, and the copolymer in the coating are prepared from the same monomers, it is to be understood that the copolymer in the coating has a melting point of less than about 50.degree. C. or is noncrystalline, that is amorphous. It is to be further understood that this description applies by implication to the description of the invention in the claims.
In a more specific embodiment, the suture or ligature is manufactured from a homopolymer prepared from the monomer glycolide. In another more specific embodiment, the suture or ligature is manufacture from a homopolymer prepared from the monomer lactide. In yet another more specific embodiment, the suture or ligature is manufactured from a copolymer prepared from the monomers glycolide and 1,3-dioxan-2-one. In a further specific embodiment, the suture or ligature is manufactured from a copolymer prepared from the monomers glycolide and lactide.
The suture or ligature can be in multifilamentary form. In a specific embodiment, the coating comprises about 1/10 to 5% by weight of the coated multifilamentary suture or ligature. In a more specific embodiment, the coating comprises about 1/2 to 3% by weight of the coated multifilamentary suture or ligature. In the more specific embodiment, the coating can comprise up to about 11/2 percent by weight of the coated multifilamentary suture or ligature.
A process for coating a bioabsorbable surgical article has also been invented. The process comprises dissolving in acetone a random copolymer, from about 65 to 85 percent by weight of the copolymer consists of linkages of formula (I): ##STR5## and the remaining linkages comprise at least one of the formulas (II) and (III): ##STR6## contacting the surgical article with the dissolved copolymer; maintaining the contact between the surgical article and dissolved copolymer until the copolymer on the surgical article comprises from about 1/10 to 5% by weight of the coated surgical article; removing the coated surgical article from the dissolved copolymer; and drying the copolymer coating on the surgical article. Parameters to be used in the maintaining step are more fully described, e.g., in U.S. Pat. Nos. 4,716,203, 4,711,241 and 4,047,533, all of which are incorporated herein by reference. It is to be understood that the amount of pickup described in these patents can be increased or decreased by any person skilled in the art without undue experimentation. As a general statement, only one pass is required to obtain a coating comprising less than about 2 percent by weight of the coated strand. For a coating comprising more than about 2 percent to about 4 percent by weight of the coated strand, two passes are generally found to give a more uniform coating level. For coating levels from 4 to 5 percent, three passes will probably give the most uniform coating level.
In one embodiment, the caprolactone is .epsilon.-caprolactone.